1. Field of the Invention
This invention relates to panoramic optical systems, and more particularly to a panoramic zoom lens assembly.
2. Description of the Prior Art
A widely used method for providing continuous surveillance over a predetermined area is by video transmission. The must elemental video surveillance system consists of a single camera connected to a video monitor through a closed circuit transmission line. The video camera converts the virtual image of the area being scanned into electrical impulses which make up the video signal. In the surveillance of panoramic scenes it has been customary to use a single camera mounted on a support and rotatable about a vertical axis whereby a succession of images representative of the panoramic view are produced. In such systems the video camera is focused at successive points and therefore is not capable of monitoring all points within the panoramic scene simultaneously.
Complete acceptance and widespread use of the foregoing approach has been limited by the complexity and expense of equipment required to provide continuous surveillance of multiple locations. To minimize the equipment required, a panoramic optical lens has been developed which produces a virtual image of a panoramic view in the form of a continuous annular projection.
The annular image is projected upon the target surface of a video camera and is scanned in a horizontal scanning pattern. The image reproduced in the video receiver is an exact duplicate of the annular image including a central region of the raster surface of the video receiving tube which is unused. In order to make efficient use of the raster surface of the video picture tube, the annular image is "spread" or transformed into a rectangular image in which the complete panoramic view is portrayed on the receiver screen without image inversion, as set forth in my co-pending U.S. patent application Ser. No. 159,613, filed June 16, 1980, now U.S. Pat. No. 4,327,312 entitled "Circular Raster Sweep Generator".
A panoramic reflector has been developed which includes an outer circumscribing reflective surface of revolution, the axis of which is concentric with the viewing axis and is thus perpendicular to the image plane. The reflective surface of such lens is typically coated with a reflective material and the incoming rays are imaged in the form of an annulus on the focal plane. Conventional panoramic reflectors of the foregoing type have been limited somewhat because of image distortion and washout due to light ray interference, as well as the lack of ability to focus the image on the image plane. In particular, prior art panoramic reflector systems have heretofore not provided zoom focusing capability.